Between Jan. 1 and Sept. 7, there have been 130 reported rapes in the city, compared with 94 over the same period last year, according to statistics presented at City Hall this week.

Police officials said they did not know what exactly is driving the numbers, but believe it is an increase in reports of acquaintance rapes, such as date rape.

"We're trying to determine what the issue is," Acting Deputy Chief John Goldberg told a Board of Supervisors committee. He said rape is significantly underreported, and he thinks outreach by the department with advocacy groups may have spurred the increase in reports.

"This is not an increase ... in forced sexual assaults," Goldberg said.

He promised a "more thorough and complete analysis" for the supervisors at the next Public Safety Committee meeting.

Janelle White, executive director of San Francisco Women Against Rape, said she has not seen a dramatic increase in the number of people contacting her organization. She said she would need more specific information about the rape reports before she could speak to what is driving the increase.[Mark Godsey]